1. Technical Field
The present invention relates to a lens apparatus including a movable lens unit forwardly and backwardly moving along an optical axis in a lens barrel, and a TV camera including the lens apparatus.
2. Related Art
A lens apparatus mounted in a TV camera such as an ENG (Electronic News Gathering) camera or a cine camera includes a movable lens unit, such as a zoom lens group, forwardly and backwardly moving along an optical axis in a lens barrel. The lens barrel includes a fixed barrel for supporting the movable lens unit to be forwardly and backwardly movable around the optical axis, a cam barrel supported to the fixed barrel to be rotatable around the optical axis, and an operation ring for operating the rotation of the cam barrel. The movable lens unit is engaged in the cam barrel and forwardly and backwardly moves by rotation of the cam barrel. A lens apparatus, in which the operation ring is driven by a servo motor, has been known (for example, refer to JP-A-9-80289).
When the lens barrel is slanted, torque is generated to the cam barrel due to the self-weight of the movable lens unit. If the operation ring is driven by a motor as in the lens apparatus described in JP-A-9-80289, even if the motor is loaded, and torque is generated to the cam barrel due to the self-weight of the movable lens unit, rotation of the cam barrel is prevented. However, if the lens apparatus does not include a motor, the cam barrel may be rotated so that the movable lens unit forwardly and backwardly moves.
If the friction between the fixed barrel and the cam barrel increases, even if torque is generated to the cam barrel due to the self-weight of the movable lens unit, the rotation of the cam barrel can be prevented, so that the movable lens unit can be prevented from forwardly and backwardly moving. However, a strong force is required to rotate the cam barrel, thereby deteriorating the operability to forwardly and backwardly move the movable lens unit.